A tensile test is arguably the most useful single mechanical test that can be performed to evaluate the utility of an engineering or engineered material. Both elastic modulus and yield strength are measured by performing a tensile test.
Small scale material applications, i.e., those implicating materials having a dimensional tolerance within the range of about 10−2 to 10−9 meters, are proliferating, with nanoscience and nanotechnology being a well known area of particular focus, and discovery. Nanotechnology, or, as it is sometimes called, molecular manufacturing, is a branch of engineering that deals with the design and manufacture of extremely small devices built at the molecular level of matter. The Institute of Nanotechnology in the U.K. expresses it as “science and technology where dimensions and tolerances in the range of 0.1 nanometer (nm) to 100 nm play a critical role.”
As there is no clear correlation between macroscopic and microscopic material properties, the ability to assess the mechanical properties of nano-scale devices or materials would no doubt reveal at least subtle properties of materials previous thought to be well defined. Initial design and prototype phases of nanotechnological product development are direct beneficiaries of instruments and/or systems for assessing mechanical properties of micro/nano materials.
Unlike other mechanical test regimes, tensile tests have the advantage of uniform stress and strain fields, which is why they are used to determine mechanical properties at larger scales. However, conventional tensile tests have disadvantages at smaller scales in that smaller forces are required, and specimen gripping, which is a function of specimen type and geometry, is often difficult.
A variety of challenges are manifest in the testing of small specimen, i.e., those in the millimeter to sub-millimeter range, especially alignment of such specimens with a tensile axis. Peer-reviewed tensile test literature recommends that a given specimen be aligned within a 3-degree range of the tensile axis so as to achieve accurate stress-strain data. As should be readily appreciated, for a specimen of a nominal 1 mm length, a non-Z-axis error of less than 53 μm, or less than 530 μm for a 10 mm specimen is required.
As is well known, there exists a variety of ever increasing small-specimen tensile testing applications, for example, and without limitation: single and multi-component nanocomposite fibers, textiles and plastics; biomedical materials (e.g., sutures, guidewires, signal wires, prosthetic and implantable material); biological materials (e.g., blood vessels, muscles, tendons, organ tissue, skin, etc.); and, biomimetic investigations (e.g., spider silk). Furthermore, and likewise, small-scale pull applications abound, and include, without limitation, stiction, adhesion, deflection and deformation of thin film systems comprising micro-electro-mechanical systems (MEMS); microelectronics interconnection components (e.g., wire conductors, PCB traces, and solder, pad and wirebond adhesion); and, biomedical coating, component and system interface adhesion assessments. With this backdrop, it remains imperative, among other things, to reduce test related set up time, to improve accuracy and repeatability of small-specimen tensile testing and small-scale pull tests, and to acquire non-tensile axis test data in furtherance of automated specimen assessment and alignment, as well as in connection to additional failure mode assessment.